Re: [PATCH v3] selftests/x86: Support Atom for syscall_arg_fault test

[shuah <shuah@kernel.org>]

Hi Bo,

On 5/17/19 1:02 AM, Tong, Bo wrote:
> Is this patch going to be merged? Or still any blocking issue there?
> 
> Thanks,
> Bo
> 
> -----Original Message-----
> From: shuah [mailto:shuah@kernel.org]
> Sent: Friday, April 19, 2019 10:05 PM
> To: Tong, Bo <bo.tong@intel.com>; luto@kernel.org; x86@kernel.org
> Cc: linux-kselftest@vger.kernel.org; linux-kernel@vger.kernel.org; skhan@linuxfoundation.org; shuah@kernel.org
> Subject: Re: [PATCH v3] selftests/x86: Support Atom for syscall_arg_fault test
> 
> On 4/19/19 1:10 AM, Tong Bo wrote:
>> Atom-based CPUs trigger stack fault when invoke 32-bit SYSENTER
>> instruction with invalid register values. So we also need SIGBUS handling in this case.
>>
>> Following is assembly when the fault exception happens.
>>
>> (gdb) disassemble $eip
>> Dump of assembler code for function __kernel_vsyscall:
>>      0xf7fd8fe0 <+0>:     push   %ecx
>>      0xf7fd8fe1 <+1>:     push   %edx
>>      0xf7fd8fe2 <+2>:     push   %ebp
>>      0xf7fd8fe3 <+3>:     mov    %esp,%ebp
>>      0xf7fd8fe5 <+5>:     sysenter
>>      0xf7fd8fe7 <+7>:     int    $0x80
>> => 0xf7fd8fe9 <+9>:     pop    %ebp
>>      0xf7fd8fea <+10>:    pop    %edx
>>      0xf7fd8feb <+11>:    pop    %ecx
>>      0xf7fd8fec <+12>:    ret
>> End of assembler dump.
>>
>> According to Intel SDM, this could also be a Stack Segment Fault(#SS,
>> 12), except a normal Page Fault(#PF, 14). Especially, in section 6.9
>> of Vol.3A, both stack and page faults are within the 10th(lowest
>> priority) class, and as it said, "exceptions within each class are
>> implementation-dependent and may vary from processor to processor".
>> It's expected for processors like Intel Atom to trigger stack
>> fault(SIGBUS), while we get page fault(SIGSEGV) from common Core processors.
>>
>> Signed-off-by: Tong Bo <bo.tong@intel.com>
>> Acked-by: Andy Lutomirski <luto@kernel.org>
>> ---
>>    tools/testing/selftests/x86/syscall_arg_fault.c | 10 ++++++++--
>>    1 file changed, 8 insertions(+), 2 deletions(-)
>>
>> diff --git a/tools/testing/selftests/x86/syscall_arg_fault.c
>> b/tools/testing/selftests/x86/syscall_arg_fault.c
>> index 7db4fc9..d2548401 100644
>> --- a/tools/testing/selftests/x86/syscall_arg_fault.c
>> +++ b/tools/testing/selftests/x86/syscall_arg_fault.c
>> @@ -43,7 +43,7 @@ static sigjmp_buf jmpbuf;
>>    
>>    static volatile sig_atomic_t n_errs;
>>    
>> -static void sigsegv(int sig, siginfo_t *info, void *ctx_void)
>> +static void sigsegv_or_sigbus(int sig, siginfo_t *info, void
>> +*ctx_void)
>>    {
>>    	ucontext_t *ctx = (ucontext_t*)ctx_void;
>>    
>> @@ -73,7 +73,13 @@ int main()
>>    	if (sigaltstack(&stack, NULL) != 0)
>>    		err(1, "sigaltstack");
>>    
>> -	sethandler(SIGSEGV, sigsegv, SA_ONSTACK);
>> +	sethandler(SIGSEGV, sigsegv_or_sigbus, SA_ONSTACK);
>> +	/*
>> +	 * The actual exception can vary.  On Atom CPUs, we get #SS
>> +	 * instead of #PF when the vDSO fails to access the stack when
>> +	 * ESP is too close to 2^32, and #SS causes SIGBUS.
>> +	 */
>> +	sethandler(SIGBUS, sigsegv_or_sigbus, SA_ONSTACK);
>>    	sethandler(SIGILL, sigill, SA_ONSTACK);
>>    
>>    	/*
>>
> 
> In case there is a dependency on x86 tree, here is my Ack
> 
> Acked-by: Shuah Khan <skhan@linuxfoundation.org>
> 

Looks like it got left behind in the confusion of which tree.

I will apply this to my tree.

thanks,
-- Shuah